People are generally aware of the most common causes of hallucinations, like schizophrenia and a really high fever. But lesser known are the more rare causes; here are six you probably haven't heard about.

Following the potential anthrax exposure affecting an estimated 84 workers at the Centers for Disease Control and Prevention(CDC) in Atlanta, head of the CDC's Bioterror Rapid Response and Advanced Technology Laboratory, Michael Farrell, has been reassigned, Reuters reported. Due to the possibility of infection, CDC employees who may have been exposed to the deadly disease have been forced to receive a vaccine and powerful antibiotics as a protective measure.

"Out of an abundance of caution, CDC is taking aggressive steps to protect the health of all involved, including protective courses of antibiotics for potentially exposed staff," Tom Skinner, a spokesman for the agency, told NBC News. "Based on most of the potential exposure scenarios, the risk of infection is very low."

Anthrax is serious infectious disease caused by the Bacillus anthracis bacteria that can be found naturally in soil where it commonly affects domestic and wild animals around the world. Although it is not contagious like the cold or flu, it can cause severe illness among humans who come in direct contact with anthrax spores. Anthrax spores can enter the body through inhalation, an open wound, or contaminated food and drink.

According to the CDC, the inadvertent exposure that was discovered on June 13 occurred after workers failed to practice proper safety precautions including personal protective equipment while handling live B. anthracis. The workers who thought they were handling inactivated anthrax samples were immediately informed of the possible exposure after traces of live anthrax bacteria were found on the original bacterial plates.

As part of an internal investigation, scientists at the CDC have conducted a thorough analysis of samples taken from possibly contaminated surfaces. Although the first two days of testing employees for possible exposure have turned up negative, the CDC will continue to watch sample for another six days while testing for anthrax activity.

"No employee has shown any symptoms of anthrax illness," director of the environmental health and safety compliance office at the CDC, Dr. Paul Meechan told Reuters. "This should not have happened. We're taking care of it. We will not let our people be at risk."